Regeneration method of heterogeneous catalysts and adsorbents

ABSTRACT

Process for the regeneration of a solid catalyst or of a solid adsorbent wherein the catalyst or the adsorbent is used in the form of a bed in a regeneration zone, in which bed the catalyst is in motion, said process comprising at least one heating step under a reductive atmosphere.

DESCRIPTION OF THE INVENTION

[0001] Process for the regeneration of a solid catalyst or of a solidadsorbent wherein the catalyst or the adsorbent is used in the form of abed in a regeneration zone, in which bed the catalyst is in motion, saidprocess comprising at least one heating step under a reductiveatmosphere.

PRIOR ART

[0002] Heterogeneous catalysts and adsorbents are used in a number ofapplications in refining, petrochemicals and chemicals industries. Theyshow their full performance at start of run, but after some time onstream usually deactivate more or less slowly depending on theapplication and the conditions of use. One reason of this activity lossis the formation of carbon deposits, typically called coke, restrictingeither the access or the nature of the active sites. A well-knowncountermeasure is the removal of these deposits by a controlledcombustion, usually called regeneration. This operation can be performedeither inside the reactor (in-situ method), either outside in adedicated unit. For fixed bed units, this last method is more and morepracticed for a number of reasons, as better temperature control leadingto a higher activity recovery, time savings, environmental constraints.

[0003] Another reason of deactivation of catalysts and adsorbents,especially those containing transition metals, is the poisoning of themetallic phase by various compounds brought during the run by thefeedstock, one common poison being sulfur-containing molecules. GroupVIII metals, either precious, as Platinum or Palladium, or not, asNickel, are known to be deactivated by the adsorption of Sulfur.

[0004] The typical off-site regeneration techniques are based on acontrolled combustion under diluted oxygen in various moving bedsystems, either rotary furnaces such as Rotolouvres (U.S. Pat. Nos.4,551,437 or 4,605,371), or belt furnaces and fluidized bed systems(EP-A-1002 581). One of the key elements of the process is to controloxygen partial pressure, which in turn governs the kinetics of carbonelimination and thus the heat release from the oxidation reactions. Thisoperation of regeneration has often to be preceded of stripping stepconsisting of heating step, either under air or inert atmosphere(nitrogen or lean gas) in order to eliminate some free hydrocarbonscontained in the catalyst porosity, just by promoting a phenomenon ofevaporation.

INVENTION

[0005] It has now been discovered that this conventional technique couldbe significantly improved in a number of cases by adding a heating stepunder a hydrogen-containing atmosphere before an optional oxidativestep. In some cases the hydrogen treatment alone can be sufficient torestore the catalyst or adsorbent activity. This process can be appliedon any type of heterogeneous catalysts or adsorbents either made of anamorphous or crystalline material as for instance a zeolite. Thisthermal treatment with an hydrogen containing gas can be associated withother treatment steps, such as oxygen containing gas treatment, or inertgas treatment, or solvent extraction for removal of leachable impuritiesor an association of these steps.

[0006] This step in the presence of hydrogen containing gas seemsspecifically useful for some metal containing catalysts, specificallywhen metals belong to Group VIII type, such as for instance Platinum,Palladium or Nickel. The process applies also for some adsorbents, forinstance Nickel containing adsorbents that are used for example assulfur traps for purification of hydrocarbon feedstocks. After some timeon stream they are more or less deactivated, meaning that their Sulfuradsorption capacity is greatly diminished. The new procedure accordingto this invention involving a treatment under hydrogen containing gaswould be more efficient for restoring the adsorption capacity than aconventional regeneration with an oxidizing atmosphere.

[0007] In order to implement the process according to the presentimprovement, it is rather essential that during said process, theparticles of the catalyst or of the adsorbent, i.e. the catalyst bed orthe adsorbent bed, is in motion, said beds being selected for instancefrom the group consisting of mobile or moving beds, circulating beds,slurry beds, fluidized beds, expanded beds, ebullated beds or beds suchas belt beds or rotary beds.

[0008] This treatment in a reductive atmosphere has proved to besuperior to the conventional oxidative one step treatment. It is alsobetter than a two step treatment consisting of Nitrogen followed by anOxygen containing atmosphere. It appears that in some cases Hydrogen ismore efficient than air for the removal of some types of carboncontaining compounds, and also more efficient than Nitrogen. When thereductive treatment is not sufficient for removing all the carbonaceousspecies, then a subsequent oxidative treatment (conventional forinstance) may be needed. In this case the residence time needed forcompleting carbon elimination is very much shortened compared to adirect oxidative treatment alone.

[0009] In the prior art, the oxidative treatment takes place attemperature between 300° C. and 700° C., and more typically between 400°C. and 600° C. The stripping step under air or nitrogen may be performedin a wider range of temperatures, depending on the boiling points ofhydrocarbons to be stripped, typically between 20° C. and 500° C. Thishydrogen treatment step according to the invention can also beenpracticed in the low range of temperatures, i.e. around 20-200° C. Inthis case the main phenomenon involved is mainly a stripping under a nonoxidative atmosphere and the benefits of using Hydrogen instead ofNitrogen would be rather narrow. On the other hand, it has been foundaccording to an improvement of the present invention that the use ofhigher temperatures such as 250 to 650° C. and more specifically 300 to550° C. brings a specific advantage.

[0010] Applications

[0011] The benefits of the invention are probably most visible when thecoke deposit has some aliphatic character, which is the case forinstance if catalyst has been used in an application at rather lowtemperature under hydrogen pressure. One example where such conditionsare used is the process of selective hydrogenation of olefinic cutsdownstream a steam cracker. Catalysts used for these applicationscontain Palladium, alone or associated with a second metal (e.g. Silveror Gold), finely dispersed on a support, often alumina based. Typicalcatalysts for the C2 or C3 cut treatment contain a low Palladium amount(less than 0.1% weight). One side reaction is the so-called formation ofgreen oil, these long chain oligomers being still often found in theporosity of these deactivated catalysts. The operation of regenerationwill have to take place at moderate temperature, due to the intrinsicsensitivity of these materials. A conventional regeneration in oxidativeconditions, either with or without nitrogen stripping, may produce inthese low temperature conditions a product with some gray to blackzones, so still containing some traces of carbon. On the other hand, apretreatment with hydrogen will remove a large part of carbon and thesubsequent oxidative step can thus be much easier.

[0012] Another case of application of this new regeneration method canbe for the catalysts used in aromatics hydrogenation, for examplebenzene transformation to cyclohexane, or hydrogenation of various otherheavier aromatics containing feedstocks. These catalysts are oftencontaining a rather high amount of Nickel, typically 30 to 60 wt %.Another case where the carbon deposit can have a somehow aliphaticcharacter is encountered with shape selective zeolites used for varioushydrocarbon transformations. Their internal porosity of channels andcavities of these crystallized aluminosilicates is small enough to limitthe formation of polyaromatic rings by steric hindrance. One well-knowncase is the zeolite ZSM5 (or the approaching structure Silicalite) witha channel dimension around 5.5 Angstroms. So this method can also beused with profit for regeneration of aluminosilicates. Anotherapplication of this invention is for the reactivation of the adsorbentscalled in the industry as Sulfur traps. In the refining or petrochemicalindustry, some catalysts extremely sensitive to sulfur need to beprotected by a Sulfur guard bed. For instance, between a naphthahydrotreater and the reformer or the isomerizer downstream, a “SulfurGuard Bed” protects the Platinum containing catalysts loaded in theseunits. Its role is to remove sulfur compounds present in hydrotreatednaphtha feedstock, as mercaptans, thiophene or hydrogen sulfide. Thesecompounds are found at concentrations typically below 1 part per millionin normal operation, and potentially higher during some upsets of thenaphtha hydrotreating unit. Some sulfur guard beds are also installed inthe chemical industry in order to protect hydrogenation catalystscontaining either precious metals (Pt, Pd), nickel or copper chromites.In most cases, hydrogenation units consist of several reactors in seriesin which the first one usually plays the role of adsorbing sulfurcompounds of the feedstock. Some nickel hydrogenation catalysts can befully deactivated after adsorption of 1 wt % sulfur. The most commonsulfur traps available on the market are nickel-based materials, withtypically a Nickel content of 20 to 60 wt %. They exhibit a high sulfuradsorption capacity for H₂S and mercaptans as well as a lower affinityfor thiophenes. The nickel containing traps, once contaminated withSulfur has to be discarded. To the best of our knowledge, there is notechnique allowing restoring the properties of a spent sulfur material.The conventional techniques of high temperature treatment either undernitrogen or under oxygen containing atmosphere are not able to restorethe adsorption properties of these spent materials, even if a partialsulfur elimination can be observed. It has now been discovered that aheating step under a hydrogen-containing atmosphere could somehowrestore the adsorption properties for Sulfur contaminated Nickel trapsmore efficiently than conventional techniques.

EXAMPLE 1 Comparative

[0013] A spent Nickel based material, used as a sulfur absorbent forlight hydrocarbon feeds, was used to evaluate various regenerationroutes. It contained about 52 wt % Nickel, the rest being silicon andaluminum oxide. Sulfur content is 17.2 wt %, measured by a LECOanalyzer, and hydrocarbons content, measured by weight loss underNitrogen up to 500° C. in a Setaram thermobalance is 5.7 wt %. Strippingof mentioned spent catalyst is performed under nitrogen at 500° C. in alaboratory rotating furnace setup. Catalyst feedrate is 50 grams/hourwith a residence time of 2 hours in the furnace hot zone and a flow rateof 500 liters /hour of nitrogen. After the treatment, the hydrocarbonanalysis is below 0.5 wt % and Sulfur content is 17.6 wt %. Thisprocedure does not reduce the sulfur but removes light hydrocarbonspecies. The product is then submitted to an adsorption test using butylmercaptan. This sulfur molecule is chosen as light naphtha feedstocktypically contains mercaptans and thiophenes. The procedure is thefollowing: 5 grams of catalyst are heated up to 180° C. and kept therefor 4 hours, with a gas (10 liters/hour) containing 10 mol % of butylmercaptan in nitrogen. After the test, the system is purged withnitrogen at 180° C. for 1 hour (2 liters/hour flow rate) and the sulfurcontent of the catalyst is analyzed. The sulfur uptake of this nitrogenstripped product in the mercaptan adsorption test is 6.1 wt %. This isabout ⅓ of the capacity of a fresh material in these same conditions,and thus means that the material is not very attractive for reuse.

EXAMPLE 2 Comparative

[0014] The material of example 1 is further treated at 450° C. underair. The same laboratory rotating furnace setup as mentioned in example1 is used. Catalyst feed-rate is 50 grams/hour with a residence time of2 hours at a flow rate of 500 liters/hour of air. The sulfur content isreduced to 5.6 wt %. The sulfur uptake of this air regenerated productin the mercaptan adsorption test as mentioned is 0.2 wt %, which meansthat the material is virtually inactive.

EXAMPLE 3

[0015] The air-regenerated product as obtained in example 2 issubsequently activated under hydrogen at 450° C.The same laboratoryrotating furnace setup as mentioned in example 1 is used. Catalystfeed-rate was about 50 grams/hour with a residence time of 2 hours at aflow rate of 500 liters/hour of hydrogen. Sulfur content remainsvirtually unchanged at 5.3 wt %. The Sulfur uptake of this activatedmaterial in the mercaptan adsorption test is 13.8 wt %, which means thatthe material may be qualified for a potential re-use in an industrialunit.

EXAMPLE 4

[0016] The air-regenerated product as obtained in example 2 issubsequently activated under hydrogen at 600° C., all conditions beingthe same as described in example 3 except temperature. Sulfur contentdecreases to 3.3 wt %. The Sulfur uptake in the mercaptan adsorptiontest is 15.6 wt %. Product is still better than in example 3 and is thusimproved by the high temperature treatment.

EXAMPLE 5

[0017] The raw material as mentioned in example 1 is treated directlyunder hydrogen at 600° C. The same laboratory rotating furnace setup asmentioned in example 1 is used. Catalyst feed-rate is about 50grams/hour with a residence time of 2 hours at a flow rate of 2 liters/hour of hydrogen. Sulfur content is reduced to 2.9 wt %. The Sulfuruptake of this material in the mercaptan adsorption test is 16.3 wt %,meaning that it may be qualified for a potential re-use in an industrialunit.

EXAMPLE 6 Comparative

[0018] Around 1 kg of spent catalyst applied for selective hydrogenationof ethylene cut from steam cracking is used. It contains a low amount ofPalladium, less than 0.1 wt % supported on alumina. Carbon content fromthe LECO analyzer is 4.7 wt %. It is treated according to a two-stepprocess. Stripping of mentioned spent catalyst is performed underNitrogen at 450° C. in a laboratory rotating furnace setup. Catalystfeed-rate is 50 grams/hour with a residence time of 2 hours in thefurnace hot zone and a flow rate of 500 liters/hour of nitrogen. At thispoint, Carbon content is 1.2 wt %. Then the oxidative regeneration stepis performed in the same conditions replacing nitrogen by dry air at atemperature of 450° C. At the end of the treatment, carbon content is0.1 wt % but the product still shows some black and gray shadows.

EXAMPLE 7

[0019] The raw material as used for example 6 is treated first byHydrogen at 450° C. in the laboratory rotating furnace setup. Catalystfeed-rate is 50 grams/hour with a residence time of 2 hours and a flowrate of 500 liters/hour of hydrogen. Carbon content is 0.5 wt %. Thenthe oxidative regeneration step is performed in the same conditionsreplacing Hydrogen by dry air at a temperature of 450° C. At the end ofthe treatment, carbon content is 0.1 wt % and the product ishomogeneously light gray.

EXAMPLE 8

[0020] The raw material used for example 6 is leached first by a solventin order to remove some light hydrocarbons. Around 300 g of this spentcatalyst are placed in a beaker, covered with 600 ml of white spirit andleft 1 hour at 80° C. and filtered. The wet catalyst is then treated byHydrogen at 450° C. in the laboratory rotating furnace setup. (50grams/hour in weight of dry product, residence time 2 hours, 500liters/hour of hydrogen. Carbon content is 0.3 wt % after the leachingand the Hydrogen steps. Then the oxidative regeneration step isperformed in the same conditions replacing hydrogen by dry air at atemperature of 450° C. At the end of the treatment, carbon content is0.1 wt % and the product is homogeneously light gray.

EXAMPLE 9

[0021] An activity test is performed to qualify the performance of bothproducts of examples 6 and 7 in selective acetylene removal of a mixedethylene cut. The feedstock has the following composition (expressed in% volume): Hydrogen 26.6; Ethylene 42.3; Methane 30.8%, Acetylene 0.26;Carbon monoxide 0.032. The test starts at 38° C. and temperatureincreases at 2.5° C./min. The so-called cleanup temperature T_(cu) isdetermined when the acetylene composition goes down to 20 ppm. Then atincreasing temperature ethylene gets more and more hydrogenated andrunaway can be reached. T_(ra) is noted for a 3% volume ethyleneconversion. Then, temperature is decreased back to 38° C. and thenprocedure is repeated. A new couple of temperatures T′_(cu) and T′_(ra)is determined. The difference T′_(ra)−T′_(cu) is defined as theoperating window. The best catalyst has the lowest cleanup temperatureand the largest operating window. The product of example 6 regeneratedaccording to a prior art procedure has a cleanup temperature of 50.0° C.and an operating window of 22.2° C. The product of the example 7regenerated according to the invention has a cleanup temperature of48.5° C. and an operating window of 24.9° C.

EXAMPLE 10 Comparative

[0022] A spent massive nickel containing catalyst, used in anapplication of aromatic hydrogenation, is also used to compare theconventional regeneration with the new method. It contained about 52 wt% Nickel, the rest being alumino silicate support. It is contaminatedwith 0.9 wt % sulfur and 6.7 wt % carbon. Regeneration of mentionedspent catalyst is performed under air at 300° C. in a laboratoryrotating furnace setup. Catalyst feed-rate is set at 50 grams/hour witha residence time of 2 hours in the hot part of the furnace and airflowis 500 liters/hour. The product is then fed again under air at 450° C.to the same rotating furnace set up in the same condition. The residualsulfur content of the regenerated product is 0.6 wt % while the carboncontent is reduced to 0.6 wt %. A representative sample of the productis collected, grinded and sieved between 16 and 25 ASTM sieve. A 0.5 gsample is submitted to a benzene hydrogenation test. Sample is mixedwith inert alumina of same granulometry and loaded in the basket of anautoclave from Autoclaves Engineer. Reactor is closed, purged withnitrogen for 0.5 hour. A hydrogen flow of 1 liter/h is applied andreactor is heated up to 400° C. for 4 hours with the objective ofachieving a reduced state. Reactor is then allowed to cool down underNitrogen flow to ambient temperature. At this point 50 ml of a mixture80/20 of cyclohexane/benzene is added through a calibrated pump, andcatalyst temperature adjusted to 100° C. Reactor pressure is adjustedand regulated to 1 Mpa. A gas dosage system operating at 3 Mpa ofHydrogen is connected to the reactor and the pressure of this gasburette is monitored through a pressure transducer and recorded withtime. The activity result is expressed by the rate constant of hydrogenconsumption kinetics.

[0023] Result is found for this regenerated catalyst at 12.1 10⁻³ s⁻¹.

EXAMPLE 11 Comparative

[0024] The spent catalyst as used in example 10 is regenerated under airin two steps in the laboratory rotating furnace in the same conditionsas in example 10, except temperature: first step still at 300° C., andthen second step at 550° C. The residual sulfur and carbon contents ofthe regenerated product are respectively 0.4 and 0.1 wt %. Arepresentative sample of the product is collected and submitted to abenzene hydrogenation test as described in Example 10. The sameprocedure is used including the in-situ reduction step at 400° C.Activity is measured at 10.9 10⁻³ s⁻¹. No improvement is noted with thehigher temperature despite the reduction in C and S levels.

EXAMPLE 12

[0025] The spent catalyst as used in example 11 is regenerated underhydrogen in one step in the laboratory rotating furnace at a temperatureof 450° C. Catalyst feed-rate is set at 50 grams/hour with a residencetime of 2 hours and hydrogen flow is 500 liters/hour. The residualsulfur content of the regenerated product is lowered at 0.7 wt % whilethe carbon content is reduced to 1.8 wt %. A representative sample ofthe product is collected and submitted to a benzene hydrogenation testas described in Example 10. The same procedure is used including thein-situ reduction at 400° C. Activity is measured at 14.7 10⁻³ s⁻¹.

EXAMPLE 13

[0026] The spent catalyst as used in example 11 is regenerated underhydrogen in one step in the laboratory rotating furnace at a temperatureof 550° C. All other conditions are the same than example 12. Theresidual sulfur content of the regenerated product is lowered at 0.3 wt% while the carbon content is reduced to 1.2 wt %. A representativesample of the product is collected and submitted to a benzenehydrogenation test as described in Example 10. The same procedure isused including the in-situ step reduction at 400° C. Activity ismeasured at 16.3 10⁻³ s⁻¹.

[0027] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples. Also, the preceding specific embodiments are to be construedas merely illustrative, and not limitative of the remainder of thedisclosure in any way whatsoever.

[0028] The entire disclosure of all applications, patents andpublications, cited above and below, are hereby incorporated byreference.

[0029] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. Process for the regeneration of a solid catalyst or of a solidadsorbent wherein the catalyst or the adsorbent is used in the form of abed in a regeneration zone, in which bed the catalyst is in motion, saidprocess comprising at least one heating step under a reductiveatmosphere.
 2. Process according to claim 1 wherein the said heatingstep is carried out under a non-oxydative atmosphere.
 3. Processaccording to claims 1 or 2 carried out between 250 and 650° C. 4.Process according to claim 3 carried out between 300 to 550° C. 5.Process according to one of claims 1 to 4 wherein the reductiveatmosphere is a hydrogen-containing atmosphere.
 6. Process according toone of claims 1 to 5 wherein after the reductive treatment, a subsequentoxidative treatment is carried out.
 7. Process according to any ofclaims 1 to 6 wherein the said bed in motion is selected in the groupconsisting of mobile or moving beds, circulating or slurry beds,fluidized beds, expanded beds, ebullated beds, and beds such as beltbeds or rotary beds.
 8. A process according to any of claims 1 to 7wherein the catalyst or the adsorbent contains an amorphous or zeoliticsupport.
 9. A process according to claim 1 to 7 wherein the saidmaterial contains at least one metal belonging to Group VIII.
 10. Aprocess according to claim 9 wherein the said material containspalladium.
 11. A process according to claim 9 wherein the said materialcontains nickel.
 12. A process according to claim 9 for the regenerationof a hydrogenation catalyst.
 13. A process according to claim 10 for theregeneration of a nickel-containing adsorbent.